Noncorroding arcing circuit interrupting device



Patented June 26, I951 2,558,076 ICE NON CORRODING ARCING CIRCUITINTERRUPTING DEVICE Howard M. Elsey, Oakmont, Pm, assignor toWestinghouse Electric Corporation, East Pitts burgh, Pa., a corporationof Pennsylvania Application April 23, 1948, Serial No. 22,868

Claims.

This invention relates generally to circuit interrupting devices andmore particularly to circuit interrupting devices which are subjected tocorrosive nitrogen oxides resulting from electrical discharges whichoccur during operation.

In certain applications of circuit interrupting devices whichare subjectto arcing during operation, it is necessary that the device be enclosedeither in a sealed casing or in a casing which has only a limited supplyof ventilating air For example, mine motor controllers which are subjectto considerable arcing in operation must be provided with a casing whichwill reduce the danger of explosions which might be caused by an exposedarc igniting inflammable gases in the mine atmosphere.

In such applications, it has been found that the electrical contacts andother parts of the circuit interrupting device are subject toconsiderable corrosion in service. The corrosion is especially severe ifthe device is operating in a humid atmosphere.

It is believed that thiscorrosion is caused by compounds of nitrogenwhich are formed during operation of the device. It is well known thatan electrical discharge through air will cause the nitrogen and oxygenof the air to combine to form various nitrogen oxides. These nitrogenoxides are not only extremely reactive themselves but in the presence ofwater vapor they dissolve or react to form various corrosive acids ofnitrogen. These acids of nitrogen when present in the atmosphere in thecasing will corrode and may severely damage the electrical contacts andthe circuit interrupter mechanism. Although only a small amount ofnitrogen compounds may be produced by any one are, considerable oxidesof nitrogen and acids of nitrogen may be produced during long continuedoperation.

These nitrogen compounds resulting from areing have other undesirableefiects in other types of circuit interrupting devices. For example, ininternal combustion engine distributors the nitrogen acids are formed inthe atmosphere within the distributor housing by the sparking betweenthe rotor and the spark plug wire terminals. The acids thus formedaccumulate upon the walls of the housing, wetting the wall surface,thereby reducing the surface dielectric strength which may result inshort circuiting, and thus causing failure of the ignition system.

The object of this invention is to provide for prevention of corrosionin enclosed circuit interrupting devices which are subject to electricaldischarges during operation.

A more specific object of this invention is to provide for removingnitrogen oxides and nitrogen acid vapors fromencased circuitinterrupting devices.

For a fuller understanding of the nature and objects of the invention,reference should be had to the accompanying drawing, in which:

' features of the invention;

Figure lis a view in elevation partly in cross- .section of a circuitinterrupter embodying the and Fig. 2 is a view in elevation partly incrosssection of an internal combustion engine distributor housing whichembodies the features of the invention.

It has been found that certain chemical compounds with a strongoxidizing power are capable of reacting with nitrogen oxides andnitrogen acids as rapidly as they are produced in circuit interruptingdevices. Such compounds, when present within a casing containing acircuit interrupting device which is subject to arcing and production ofnitrogen compounds during operation, will react with the nitrogencompounds to remove them from the atmosphere within the casing rapidlyenough to prevent them from damaging the electrical contacts and otherparts of the mechanism.

In practicing the invention, it is preferred to use a permanganate ofeither potassium or silver or a. mixture of both as the chemical agentto react with the nitrogen compounds. These compounds are unusual forthis purpose in that they are neither corrosive, volatile nordeliquescent, and the product of their reaction with nitrogen oxides ornitrogen acids are likewise neither corrosive, volatile or deliquescent.They react extremely rapidly with the nitrogen compounds produced byelectrical discharges.

In one embodiment of the invention, a sheet of asbestos board or otherabsorbent solid, preferably an inorganic material, is saturated with aconcentrated aqueous solution of potassium permanganate or silverpermanganate or a mixture thereof, and allowed to dry. In this mannerthe asbestos board may be impregnated with the dry salt. Glass fiber,mat, refractory sheets, felt, and other porous materials may be soimpregnated. This board is then incorporated in an encased circuitinterrupting device in any suitable manner.

Referring now to Fig. 1 there is illustrated a circuit interruptingdevice In which comprises a pair of contact members l2 and I! mounted oncontact arms l6 and I8, respectively. The contactarm I6 is suitablymounted on a supporting arm 19 to allow it to pivot about a pin 20 and aspring 22 is provided to bias the contact arm IE to the open position.An armature It is provided to draw the contact arm l6 into the closedposition when the armature 24 is energized. Disposed about the circuitinterrupting device mechanism is a casing 26 on the inner surface ofwhich is mounted sheets 28 of asbestos board held in place by screws 29,which have been impregnated with potassium or silver permanganate ashereinbefore described.

In operation the contact members l2 and it make and break the electricalcircuit by movement of the contact arm l6, which movement is controlledbythe armature 24 and the biasin spring 22 in a manner well known intheart. Whenthe contact member I2 is moved out of contact withthe memberI4 an arc is momentarily formed therebetween due to the suddeninterruption of the electric current. The passage of the arc through theair between the members l2 and I4 causes chemical reaction to occurbetween the nitrogen and oxygen in the air to form corrosive compoundsof nitrogen. The air and corrosive gases are heated by the arc and willtend to rise toward the upper surface of the casing 26 and come incontact with the asbestos board 28 where they react with the potassiumor silver permanganate embodied therein and are thereby removed from theatmosphere.

To enable the asbestos board to be replaced when required, it isdisposed in place by the screws 29 in such a manner as to allow it to beasily removed.

Referring now to Fig. 2 there is illustrated an internal combustionengine distributor 30 having a housing 32 formed of a dielectricmaterial such as mica-impregnated phenol condensate or hard rubber andhaving individual spark plug terminals 34 arranged around the peripheryof the housing 32. One terminal 34 is provided for .each spark plug ofthe engine and is connected thereto by means not shown for simplicity indrawing. Current is conducted to the individual spark plug terminals 34by means of a conventional distributor rotor 38. Disposed on the innersurface of the housing 32 is a layer of asbestos board 36 which has beenimpregnated with potassium or silver permanganate as hereinbeforedescribed.

During operation of the distributor, the rapid making and breaking ofthe circuit to the individual spark plugs by the rotor contact (notshown) with the spark plug terminals 34 causes almost continuoussparking. This sparking forms deleterious nitrogen compounds aspreviously described which react with the potassium permanganatedisposed in the asbestos board thereby preventing them from attackingthe contact surfaces of the terminals 34- and from wetting the interiorsurface of the housing 32.

It is to be understood that the illustrated methods of incorporating theinvention into a circuit interrupting device are exemplary only and I donot limit myself to these specific means since other methods may beused. For example, in either embodiment of the invention solid potassiumor silver permanganate or a mixture thereof may be encased in a porouscontainer such as a tube made of wire mesh and'the container may besuitably positioned within the circuit intersome rial selected from atleast one of the group consisting of potassium permanganate and silverpermanganate disposed in-the. casing for contact by the corrosivenitrogen compounds to remove them by reaction therewith to formnon-deleterious compounds and thereby prevent them from damaging thecircuit interrupting device.

2. An electrical circuit interrupting device comprising, in combination,a casing, electrical contacts disposed in the casing, the electricalcontacts being subject to electrical discharges through air therebetweenwhereby oxides of nitrogen are produced, and an asbestos board Iimpregnated with potassium permanganate disposed in the casing forcontact with the oxides of nitrogen produced, whereby the oxides ofnitrogen react with the potassium permanganate to form non-corrosivecompounds.

3. An electric circuit interrupting device comprising, incombination, acasing. electrical contacts disposed in the casing, the electricalcontacts being subject to electrical discharges through air therebetweenwhereby oxides of rupting device casing, preferably in such a manner topermit it to be easily replaced.

Since numerous changes may be made in the above-described constructionand diiferent embodiments of the invention may be made withnitrogen areproduced, and a porous member impregnated with potassium permanganatedisposed in the casing for contact with the compounds of nitrogenproduced, whereby the compounds of nitrogen react with the potassiumpermanganate to form non-corrosive relatively inert compounds.

4. An ignition distributor for internal combustion engines comprisingspark plug terminals disposed within a housing, a rotor for making andbreaking an electrical circuit with the spark plug terminals wherebyarcing is produced within the housing by the making and breaking of theelectrical circuit, the arcing forming corrosive compounds of nitrogenwithin the housing, and a material selected from at least one of thegroup consisting of potassium permanganate and silver permanganatedisposed within the housing for contact by the corrosive nitrogencomlected from at least one of the group consisting of potassiumpermanganate and silver permanganate disposed within the housing forcontact by the corrosive nitrogen compounds whereby the nitrogencompounds are reacted to noncorrosive, non-deliquescent substances.

HOWARD M. ELSEY.

REFERENCES orrEn The following references are of record in the file ofthis 'patent:

UNITED STATES PATENTS Number Name Date 1,421,271 McNeil June 27, 19221,716,479 Bilsky June 11, 1929 1,783,784 Grondahl et al Dec. 2, 1930FOREIGN PATENTS Number Country Date 312,002 Germany May 1919

